Television Receiver and Electronic Device

1. A tamper-detecting television receiver, comprising: a casing comprising a casing cover and a casing body, a video input within said casing for receiving an encrypted digital or analog video signal, a decoding circuit within said casing for decrypting such encrypted video signal, a video display unit inside the casing, for displaying an image corresponding to said decrypted video signal, a cover opening/closing detector for detecting an open or closed state of the casing cover; and a switch for controlling a power supply voltage that is applied to the decoding circuit, in accordance with an output of the cover opening/closing detector; wherein power is supplied to the decoding circuit through the switch when the output of the cover opening/closing detector indicates that the casing cover is closed, and the supply of power to the decoding circuit is cut off by the switch when the output of the cover opening/closing detector indicates that the casing cover is opened, and said cover opening/closing detector comprises: a condenser means; a charging means for charging the condenser means; a discharging means for discharging the condenser means when the casing cover is opened; and an opening detection means for recognizing that the condenser means is discharged, thereby detecting that the casing cover is opened.

2. A television receiver according to claim 1 wherein said cover opening/closing detector comprises: a code sequence generation circuit; a light emitter for converting an electric signal from the code sequence generation circuit into light, thereby generating a light signal; a light receiver for converting such light signal into a second electric signal; a light guide on the casing cover for guiding the light outputted from the light emitter to the light receiver, only when the casing cover is closed; a demodulation circuit for demodulating the second electric signal from the light receiver; and a comparison circuit for comparing the output of the code sequence generation circuit with the output of the demodulation circuit, and outputting a signal indicating that the casing cover is closed, when these outputs are equal to each other.